The present invention relates to vehicle transmissions. More particularly, the present invention relates to a hybrid transmission capable of receiving power from both a prime mover and a source of stored energy.
Previously, hybrid transmissions used epicyclic gearing to provide power from an internal combustion engine, a motor, or both, and relied on conventional automatic transmission technology such as wet clutches and torque converters to transition between drive ratios. These systems were found to provide only a limited number of available operating modes, and included unacceptable inefficiencies and sheer losses.
Attempts have been made to provide an improved hybrid transmission with a wide range of operating modes, but with limited success. For example, U.S. Pat. No. 6,837,816 to Tsai et al discloses an example of a known hybrid transmission including an epicyclic gearing assembly mounted coaxially with a single motor/generator. This configuration allows the motor/generator to supplement the torque supplied by an internal combustion engine, but fails to include a series hybrid mode of operation to simultaneously charge an energy storage device while providing a motive force from the single motor/generator. Similarly, U.S. Pat. No. 6,499,370 to Bowen discloses an automatic transmission including a manually-shifted synchromesh and two motor/generators disposed along first and second concentric input shafts. This configuration allows a motor/generator to supplement the torque supplied by an internal combustion engine, but also fails to include a series hybrid mode of operation. Likewise, U.S. Pat. No. 6,811,508 to Tumback discloses a known hybrid transmission including an epicyclic gearing assembly and two motor/generators carried on lay shafts in parallel alignment with the input shaft. This configuration allows both motor/generators to supplement the torque supplied by an internal combustion engine, but fails to include a mode of operation where a first motor/generator supplies a motive force while the internal combustion engine supplies power directed to the electric motor or charges an electrical energy storage device when the state of the charge falls below a predetermined level.
Therefore, there remains a need for an improved hybrid transmission that provides a wide range of mechanical ratios and can leverage the benefits of a hybrid vehicle. There also remains a need to provide an improved hybrid transmission suitable for operation in mechanical, parallel hybrid, series hybrid, and electrical power modes and having regenerative breaking and launch assist capabilities.